1. Technical Field
The present invention relates to an image forming apparatus which forms an image by transferring a developer image to a transferred member such as paper or a transfer belt.
2. Related Art
In a tandem-type image forming apparatus in which a plurality of photosensitive drums are arranged along the direction of movement of a transferred member, a plurality of developer images are superimposed on the transferred member. Therefore, these photosensitive drums are rotated synchronously so that the circumferential speeds of the plurality of the photosensitive drum match at the time of transfer.
Assuming that the circumferential speeds of the respective photosensitive drums at the time of transfer do not match, the transfer positions of the developer images with respect to the transferred member are shifted, so that an image formation failure such as so-called “color deviation (print deviation)” occurs, and hence the quality of the formed image is deteriorated.
Therefore, for example, an image forming apparatus in which errors in transmission of a drive force to respective photosensitive drums are reduced in comparison with a case where the plurality of the photosensitive drums are driven by a plurality of drive motors by driving drum gears provided on the plurality of the photosensitive drums respectively with a single electric motor via an intermediate gear, thereby inhibiting an occurrence of an image formation failure is known.
When the drive force of the electric motor is transmitted to the drum gear via a plurality of gears, the image formation failure may occur also due to dimensional unevenness of the gears.
In other words, (a) when a reference pitch circle of the gear is not a complete round and the radius of a reference pitch circle varies from portion to portion of the gear, the circumferential speed varies even when the angular speeds are the same. (b) When the reference pitches (dimensions between adjacent teeth) are different from portion to portion of the gear, the circumferential speed of a driven gear which meshes the gear and receives the drive force varies even when the angular speed and the radius of the reference pitch circle are the same.